Most modern diesel engines are provided with fuel injectors in a common rail configuration. In a common rail system, a high pressure pump supplies fuel at high pressure to a pressure accumulator, the common fuel rail. All the fuel injectors of the engine are supplied by the common fuel rail. In this way, one high pressure pump is sufficient. Older diesel engine systems using unit injectors have one pump for each injector. Due to the higher pressure used in modern diesel engines, there are increased requirements on the sealing between the injector and the cylinder head. Since the injector must be possible to remove for inspection and replacement, the sealing must be completely tight when the injector is mounted. At the same time, it must be possible to remove the injector for inspections and to replace the injector without damage to the cylinder head.
One way of solving, or at least improving this problem is to use a separate injector sleeve that is mounted in the cylinder head and in which the injector is mounted. In diesel engines using unit injectors having a relatively low pressure, deformable injector sleeves may be used. One example of such a solution is described in U.S. Pat. No. 3,334,617, in which an injector assembly including an injector-receiving copper tube extending through the coolant water jacket is shown. The sealing force is obtained by clamping the injector against an annular surface of the tube interior, where the tube end is deformed into a counter bore on the cylinder head surface. Resilient sealing means are also used to prevent leakage through the upper wall opening of the cylinder head. The deformable injector tube is deformed during installation by the clamping force of the injector in order to retain the injector tube in the cylinder head and to form a combustion seal. In order to remove the injector tube, the injector tube must be destroyed because the deformation of the injector tube makes it impossible to remove the injector tube intact. During removal, there is a risk that fragments of the injector tube may fall into the combustion chamber leading to possible failure of the engine. The removed injector tube must be discarded and must be replaced with a new component.
Further, the use of a deformable injector tube may decrease the long term stability of the injector assembly since the material may deflect over time and may lose the sealing capability. Since the injector tube is designed to provide both the combustion seal and the cooling liquid seal, any damage to the injector tube could potentially allow both combustion and cooling liquid leakage.
EP 0654601 B discloses an injector sleeve manufactured from a relatively non-deformable material which is used in conjunction with seal rings to establish a coolant seal between the cooling liquid jacket and a fuel injector. An injector cone has a tapered lower portion which is seated in a frusto-conical portion disposed within a cylinder head to establish an independent combustion seal. In this way, a separate coolant seal for the cooling liquid is provided by one part and several sealing rings, and a separate combustion seal is provided by another part. The combustion seal relies on a conical surface having a slightly smaller angle than the corresponding surface of the cylinder head.
Such a seal requires a high degree of precision during manufacture. Further, the material requires some kind of hardening treatment after the machining of the parts in order to prevent deformation of the components. Even after such a treatment, some plastic deformation may occur during use in an engine due to high pressure and high temperatures.
There is thus room for an improved injector sleeve.